Automobile manufacturing lines having a straight-line shape are widely known in the conventional technology. As an illustration thereof, individual processing areas are disposed at fixed intervals of, for example, between 10 and 20 meters in line with a processing sequence and along a manufacturing line setup with a straight-line shape. In a first processing area, an axle module is mounted on a vehicle frame having been introduced thereto. In a next processing area, this vehicle frame is temporarily hoisted up and turned upside-down, and in addition, an engine module, a transmission module, and the like are mounted thereon. In a next processing area, a fuel tank, an air tank, wiring, ducting, and the like are mounted on the vehicle frame chassis. Each time a workpiece passes through sequential processing areas in this way, new components and modules are added and mounted thereon, and the degree of completion of the workpiece as a vehicle becomes higher with each passage through a processing area. Generally, between ten and several tens of processing areas are provided along a manufacturing line, and in more specific terms, for example, 20 processing areas are provided. A system conveying an incomplete vehicle along the manufacturing line can be of a type whereby the entire line is conveyed at a slow, fixed speed, or of a type whereby a prescribed takt is set up and the incomplete workpiece is moved in steps and stopped within each processing area. In both of these cases, the operating duration during which a workpiece can be accessed in a single processing area of a manufacturing process for automobiles is between several and several tens of minutes, and for example, is 15 minutes. This time is known as the takt time. A driver boards the vehicle having been completed to a prescribed level, and the vehicle leaves the manufacturing line under its own propulsion from an end of a manufacturing line of this type.
The following is an explanation of the term “module” as used herein. The term “module” as used in this specification refers to a complex-form component constituting a single grouping assembled from a plurality of components, and the components and materials supplied to vehicle assembly processes are generally referred to as “modules”. Typical examples of “modules” are an engine module, whereupon an engine and necessary related components have been mounted, and the wheels supplied to an incomplete vehicle constituting the subject of operations in a vehicle manufacturing process. Furthermore, the fuel and other liquids supplied to an almost-complete vehicle at a final stage of a manufacturing process are also considered to be a “module”.
In contrast to the widely-implemented conventional manufacturing method as described above, the applicant of the present invention disclosed in patent document 1 a method of assembly of vehicles one (two, three, or another small number) at a time on a rotating assembly stand. In brief, the invention of patent document 1 constitutes a vehicle assembly method wherein a plurality of operations of supplying components proceed towards a single radial center and the supplied plurality of components are assembled to form a vehicle on a rotating assembly stand provided at the radial center. The gist of a device invention of the same application involves a vehicle assembly plant wherein a plurality of component supply areas are disposed in a radial pattern and a single rotating assembly stand is disposed at the radial center thereof, and providing a means for rotating that rotating assembly stand in line with the advancement of operations.
Taking the manufacture of a single truck as an example in order to supply a supplemental explanation regarding the invention of patent document 1, a disc-shaped rotating assembly stand is provided within the plant, and this rotating assembly stand is, for example, rotated at a constant speed so as to rotate once per hour, or in other words, is rotated at a constant speed of six degrees per minute. This rotating assembly stand is disc-shaped, having a diameter of, for example, between 10 and 20 meters. A plurality of module supply areas separated into substantially fan-shaped partitions are set up around that rotating assembly stand, and first of all, an axle module is delivered from a first module supply area to the rotating assembly stand. Next, a vehicle frame is delivered in a non-assembled condition from a second module supply area to this rotating assembly stand in line with the rotation thereof. This is then assembled above the axle module by a worker present on this rotating assembly stand, forming a vehicle frame. Next, the vehicle frame is mounted on the axle module. As time passes, the rotating assembly stand rotates further, and an engine module is delivered from a third module supply area, suspended in the vicinity of a front end of the vehicle frame, and mounted.
Next, a tank and piping are delivered from a fourth module supply area, and these are mounted on various vehicle components. A cab is delivered from a fifth module supply area and is mounted at a front-end section of the vehicle frame so as to cover the engine module. Various connections are made between equipment required for driving and mounted in the cab and mechanical equipment mounted on the engine module. The rotating assembly stand rotates further, and fuel, lubricating oil, and other liquids are supplied from a sixth module supply area and charged to various sections of the vehicle, now approaching completion. Furthermore, the wheels and hood are delivered from a seventh module supply area and each is mounted on the vehicle. Assembly operations reach a state of near completion when the rotating assembly stand rotates even further and the front-end section of the vehicle being assembled reaches the position of a final module supply area, and at that time, inspection devices are connected to the vehicle, the engine thereof having been started, and various inspections are carried out. The rotation position of the rotating assembly stand upon the completion of these inspections is such that the front-end section of the vehicle exactly opposes a removal path for a completed vehicle. A driver boards the vehicle and sits in the driver's seat thereof, and this vehicle leaves the rotating assembly stand under its own propulsion. When the rotating assembly stand rotates further, assembly of a next vehicle begins. That is to say, the rotating assembly stand opposes the first module supply area and an axle module is delivered.
As the new manufacturing method disclosed in patent document 1 manufactures vehicles one (two, three, or another small number) at a time in this way, the number of vehicles retained inside the plant as work-in-process and the corresponding time is markedly reduced. It has been learned that as a result thereof, significant benefits are seen in terms of interest borne in the form of work-in-process. In addition to benefits related to interest burden in the form of work-in-process, numerous other economic merits are realized through the practicing of the invention of patent document 1, and this system has been put to practical use for large-size or medium-size vehicles in a manufacturing plant of the applicant of the present invention.
Furthermore, the Kanban (signboard) system is known as a system of providing information and instruction to workers performing operations in a manufacturing process. The Kanban system is used when the specifications of a workpiece manufactured on a single manufacturing line change slightly with each unit. If the specifications of a vehicle, constituting a workpiece introduced into a single manufacturing line, are all identical, operations of fitting identical components or modules are performed repeatedly in a preset manner in all processing areas on workpieces arriving one-by-one at intervals of the takt time. In actual automobile manufacturing processes, however, specifications change slightly with each successive vehicle, even if it is assumed that all manufactured vehicles are of an identical model. In the Kanban system, a signboard is set up on a vehicle frame when the frame is introduced from the beginning of the manufacturing line. When a specific component with different specifications must be fitted as part of the fitted components, the corresponding specified specifications are displayed on this signboard so as to be easily understood by workers.
Furthermore, a mode of disposing lightning signboards in the vicinity of such a manufacturing line so as to be easily seen by workers performing operations on the manufacturing line is known in the conventional technology. These conventional lightning signboards are, for example, rectangular signboards with a landscape orientation and suspended from a ceiling so as to be capable of being commonly seen by workers from a plurality of operating process positions. Such signboards differ little from those located on platforms and at ticket barriers in departure stations of major railways, etc. and displaying messages such as, “Next train on Line x: Special Express No. yy, departing at hh:mm for zz”. The current takt-time setting (i.e., the duration that a workpiece can spend in a single processing area) and the degree to which that takt time has elapsed at the current point in time, in addition to the planned production volume for the current day, the actual number thereof completed, and other such details are displayed on these lightning signboards. In the event that a manufacturing line is stopped unexpectedly, some display the reason for the stoppage and the expected duration until recovery. Other information and instructions to be commonly supplied to a plurality of workers can also be displayed on this type of lightning signboard. The display content of conventional lightning signboards is, as a fundamental principle, modified and controlled through the operation of a manager in the plant's control room.
As background technology relating to lightning indication, patent document 2 and patent document 3 disclose a device monitoring and recording error information of manufacturing equipment under program control. Furthermore, a display device for reducing declines in capacity utilization with respect to human-induced manufacturing equipment errors is disclosed in patent document 4.
Patent document 1:JP 2004-291954APatent document 2:JP 2003-263322APatent document 3:JP 11-090795APatent document 4:JP 9-141531A